Method for reconstructing body lumens

ABSTRACT

A stent shaped as a three-dimensional body which is formed by interlaced threads ( 1 ) arranged in multistart turns of a helical line. The threads ( 1 ) are arranged in at least two groups ( 2  and  3 ) of the helical turns featuring opposite senses of helix. The stent ends are established by sections ( 5 ) where the turns of one helical line merge into those of the other helical line, said sections appearing as a single length of the thread ( 1 ).

TECHNICAL FIELD

[0001] The present invention relates in general to medicine and morespecifically to surgery and can find predominant application forendoreconstruction of blood vessels and other hollow organs andstructures of human body. The invention also enables one to carry outreconstruction of perforating lesions.

BACKGROUND ART

[0002] Modern medicine is capable of reconstructing blood vessels,ducts, and perforating lesions of human organs, using specialframework-type devices named stents. Use of stents makes it possible torestore the natural function of an defected anatomical structure withouthaving recourse to direct operative interference techniques.

[0003] In order to attain high-quality reliable endoprosthesizing saiddevices must posses a number of definite properties. First and foremoststents must provide unobstructed motion of body fluids through theimplanted structure without deteriorating metabolic processes intissues. Such stents must be rigid enough to withstand the pressureexerted by the walls of blood vessels and body cavities, to provideuniform pressure distribution over the surface being prosthesized, andthe same time possesses elasticity. Moreover, the stent constructionmust be convenient for being transported to the zone of reconstructionand positioned there, as well as must not produces any injurious effectupon the surrounding tissues in the course of implantation and furtherfunctioning.

[0004] One state-of-the-art hollow tubular stent is known to have endportions and a surface formed by a plurality of intersecting elasticelements at least part of which are interconnected at the stent ends(US, A, 733,665).

[0005] The stent can be of two different diametrical dimensions due toradial deformation of its elastic elements. Before being positioned atthe place of reconstruction the stent is deformed so as to minimise itsdiametrical dimension. Then the stent is placed, in the deformed state,inside a transporting means by arranging it on a special setting bulb.Once the stent has been transported to the place of reconstruction thesetting bulb is expanded so that the stent diameter is maximised.

[0006] It is due to its rigid construction that the stent withstandsrather high pressure of the walls of the organ being prosthesized andprovides for a uniform distribution of the resultant stresses over theprosthesized surface.

[0007] However, the stent in question features but lower elasticity dueto a restricted axial deformation, which affects the quality ofendoprosthesizing.

[0008] Another prior-art stent is known to be in the form of a hollowtubular springlike body made of a material having a shape memory effect(SME). Stents made from such a material are capable of restoring theirshape upon a change in the temperature conditions.

[0009] The advantages of said stent are determined by the properties ofthe material it is made from that provides for complete restoration ofthe stent shape in the zone of reconstruction, as well as a possibilityof its convenient withdrawal from the organ being prosthesized uponcooling of the stent. The procedure of the stent positioning isimproved, too.

[0010] A variety of stent embodiments are possible. In particular, thestent may have a construction disclosed in the aforediscussed invention(US, A, 733,665).

[0011] One more stent embodiment presents its construction as a hollowtubular element established by the coils of a wire or the turns of astrip. The construction of such a stent is more elastic since the stentis deformable both radially and axially.

[0012] However, with this stent it is not always possible to provide andoptimum value of the pitch of spring coils or of strip turns becausewith too a large pitch a uniform pressure distribution over the surfacebeing prosthesized is affected, which may result in partial vesselstenosis, whereas in the case of too a small pitch stent implantationmay cause hyperplasia of the intima of the vascular wall in the organunder reconstruction, as well as early thrombotic complications.

[0013] Still more stent of the prior art is known to appear as athree-dimensional tubular structure established by a number ofinterlaced rigid and elastic threads arranged in two groups alonghelical lines directed oppositely to each other. The ends of threads onthe end faces of the tubular structure are not connected to one anotheror to the threads of the helical coils and are arranged loosely (CH, AS,662,051).

[0014] The stent under consideration is elastic and easily deformable,and can be placed in a small-diameter delivery systems; besides, thestent provides for an adequate rigidity and a uniform pressuredistribution over the surface being proshesized.

[0015] However, the presence of free ends of threads on the end facesaffects adversely the framework properties as a whole. To attain therequired rigidity involves increasing the number of threads used, whichis undesirable since this may cause intimal hyperplasia and earlythrombotic complications. Thread ands loosely arranged on the stent andfaces produce an injurious effect upon the walls; in addition, there arerequired more complicated systems for stent transfer to the place ofreconstruction.

[0016] Known in the present state of the art is a stent in the form of athree-dimensional structure formed by interlaced threads arranged inmultistart turns of a helical line (RU, A, 1,812,980). The turns form atleast two groups featuring opposite senses of the helical line. Thethread is made of a meterial featuring the SME. The ends of threadsbelonging to different groups are fixedly joined together on the endfaces of the three-dimensional structure by, e.g., spot welding orsplicing together.

[0017] The stent under discussion provides for a required rigidity and auniform pressure distribution over the surface being prosthesized, aswell as possesses elasticity.

[0018] It is due to joined together ends of threads on the stent endfaces that its placing into a transporting system is simplified. Theselected stent material ensures virtually complete restitution of itsshape at the place of the prosthesis implantation.

[0019] However, an artificial joining of threads results in a localchange of the physic-mechanical properties of the stent, which tellsnegatively on the rigidity and reliability of the stent construction asa whole. Moreover, the presence of artificial joints between the threadson the stent end faces gives one no way of attaining a maximum possiblestent transformation which in turn places limitation on a possibility ofits placing into a small-diameter delivery systems.

DISCLOSURE OF THE INVENTION

[0020] The present invention has for its principal object to provide astent with a broad range of functional applications, possessing therequired rigidity and elasticity, as well as a high degree of the shapetransformation.

[0021] The foregoing object is accomplished due to the fact that in astent shaped as a three-dimensional body which is formed by interlacedelastic threads arranged in multistart turns of a helical line and in atleast two groups featuring opposite senses of the helix line, accordingto the invention, the ends of the three-dimensional body are establishedby the sections where the turns of one helical line merge into those ofthe other helical line, said sections appearing as a bend of a singlethread segment.

[0022] Thus, the foregoing object is attained due to the followingspecific features of the proposed construction: thfreads at the stentends have no areas of aftificial joining: merging of the turns of onehelical line into those of the other helical line appears as a bend of asingle thread segment. Hence similar physic-mechanical properties areretained in the entire stent volume, while the sections of the threadmerging at the stent ends acquire the properties of a spring and becomethe functionally active construction elements. The stent ends formed byall the aforesaid sections of the thread bend are capable ofwithstanding the pressure of the walls of the organ underreconstruction, and the stent construction acquires the requiredrigidity so that the stent provides for a uniform pressure over thesurface being prosthesized. In addition, it is due to their elasticproperties that the section of the thread bend tend to restore theiroriginal shape after their having undergone deformation, thereby takingan active part in the process of the stent shape restoration.

[0023] The herein-proposed stent construction features the requiredelasticity due to a possibility of its radial and axial deformationunder the action of small forces applied thereto.

[0024] The stent construction provides for high degree of thetransformation of the stent shape. In the case of longitudinal stentdeformation the threads slide with respect to one another, with theresult that the angle of their mutual arrangement changes, the stentdiameter decreases and becomes equal in length. Hence the stent diameteris much reduced, whereas its length changes but rather inconsiderably.High degree of the transformation cenables one to placedifferent-dimension stents into a minimised-diameter delivery systems, afuture that solves the problem of transporting stent to the place ofreconstruction along both major and minor blood vessels.

[0025] To attain the maximum degree of the stent transformation with therequired construction rigidity remaining unaffected, it is expedientthat the turns of all the helical lines are made of a single threadsegment. Such a stent possesses high elasticity and transformationability due to a low interlacing density and a small number of threads.In addition, low interlacing density tells positively on the quality ofendoreconstruction because it reduces reaction of the walls beingprosthesized to a foreign body being implanted.

[0026] It is expedient in some cases that the stent featuresvariable-pitch turns so as to provide different interlacing density asfor the stent length with a view to, eg.g., high-rate formation of theneointima of the vessel walls on individual reconstruction areas.

[0027] It is practicable that the stent is shaped as three-dimensionalbody having variable cross-section diameter as for the length thereof, afuture that makes it possible to obtain a stent shape adapted forendoreconstruction of defects of the various types and configurations.

[0028] Whenever it becomes necessary to obtain higher-density threadinterlacing on a preset area, it is expedient that the stent is providedwith additionally interwoven threads on said area. Such a stent isapplicable for, e.g., reconstructing an aneurysms vessel.

[0029] It is expedient that the free thread ends are joined on thesurface of the three-dimensional body, to the threads that form helicalturns, and/or to one another, thus adding to the stent reliability.

[0030] It is expedient that on the sections of merging, the turns of onehelical line merge into those of the helical line with the oppositesense of the helix. In this case, the radius of curvature of the mergingsection is increased, and such sections become more resilient.

[0031] A bend of the single thread segment on the merging sections mayhave various configurations, e.g., a circular arc, a loop, or anU-shape. Those merging sections are most elastic which are shaped ascircle arcs having a large radius of curvature.

[0032] In some instances it is expedient that the points of bending thethreads on the merging sections are arranged in different transverseplanes relative to the longitudinal body axis. This makes it possible toattain more compact arrangement of the stent ends during itstransformation.

[0033] It is expedient that the stent is made of a material possessing aSME or of a superelastic material. Such stent possess a virtuallycomplete degree of shape restitution.

[0034] It is expedient that, with a view to reducing itsthrombogenicity, in some instances the stent may be provided with abiocompatible material.

[0035] No sources of information have been found by the Applicants thatwould contain any data on tecnical solutions idetical or equivalent tothe device proposed herein. This, in the Applicants' opinion, rendersthe invention conforming to the condition of novelty (N).

[0036] Practical realisation of the specific features of the presentinvention imparts an important technical effect to the stent, consistingin that its required construction rigidity is attained along with highelasticity and transformation ability. The aforesaid novel feature ofthe present invention define, in the Applicants' opinion, conformity ofthe herein-proposed technical solution to the inventive step criterion(IS).

[0037] Practical use of the herein-proposed technical solution providesfor a number of positive properties that follow:

[0038] Required construction rigidity and uniform pressure distributionover the surface being prosthesized;

[0039] High stent elasticity;

[0040] High degree of the shape transformation, which enables the stentto be placed into a minimum-diameter delivery systems;

[0041] Lower traumatogenicity of the stent implanting procedure;

[0042] Broad range of functional applications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In what follows the present invention will now be disclosed in adetailed description of some illustrative embodiments thereof withreference to the accompanying drawings, wherein:

[0044]FIG. 1 is a general view of the proposal stent;

[0045]FIG. 2 shows an embodiment of the stent, wherein the bendingpoints of threads on the merging sections are situated transverse planesrelative to the longitudinal axis of the three-dimensional body;

[0046]FIG. 3 shows another stent embodiment used as a filter;

[0047]FIG. 4 shows one more stent embodiment aimed at endoreconstructionof perforating defects; and

[0048]FIG. 5 shows a stent embodiment aimed at endoreconstruction ofaneurysms vessels.

[0049] Referring now to the accompanying Drawings FIG. 1 presents astent of the present invention appearing as a three-dimensional bodymade of interlaced elastic threads 1 arranged in multistart turns alonga helical line in two groups 2 and 3 featuring opposite senses of helix.The stent is made of a single segment of the thread 1 whose loose ends 4are joined together and to the threads 1 of the groups 2 and 3 byinterlacing. The stent ends are established by sections 5 of merging theturns of the thread 1 of the group 2 into the turns of the thread 1 ofthe group 3 and appear as a bend of the single segment of the thread 1.The bend of the thread 1 on the section 5 is shaped as a circle arc.

[0050]FIG. 2 presents a stent embodiment, wherein the bending points ofthe threads 1 on the merging sections 5 are situated in differenttransverse plane's a1, a2, and b1, b2 with respect to the longitudinalstent axis and are arranged in an alternating order. The bends of thethreads 1 on the merging sections 5 are shaped as circle arcs. The stentis made from a single segment of the thread 1. Such an embodiment ispreferable for large-diameter stents used in, e.g., endoprosthesizingthe aorta, when a minimum diameter of the stent ends is to be providedin the deformed state, the required rigidity of the stent constructionremaining unaffected. The diameter of this stent can be reduced-morethan tenfold throughout its entire length. The number of turns of thethread 1 and their pitch are preset proceeding from the requiredinterlacing density, which is so selected that the area S of meshesestablished by the intersecting helical turns provides the requiredrigidity, whereas the meshes should be large enough not to causehyperplasia of the intima of the walls under reconstruction or earlierthromboses complications..

[0051]FIG. 3 presents a stent embodiment, wherein the cross-sectionaldiameter in the central portion of the three-dimensional body is muchlarger than the cross-sectional diameters of the stent ends. The stentis spherial-shaped and is aimed at use as a filter for, e.g., preventingthromboembolism of the pulmonary artery. The merging sections 5 at thestent ends are loop-shaped.

[0052]FIG. 4 presents a stent embodiment intended for reconstructing,e.g., perforating injuries of the cardiac septa, or the open arterialduct. The stent has a minimum transverse diameter at the centre of thethree-dimensional body and the maximum possible transverse diameters atits ends. The stent dimensions are so selected that its length exceedsthe maximum diameter of a defect 6, and the diameter of the stent endsis such that the projection of the stent ends onto a wall 7 exceeds thearea of the defect 6. The dotted line indicates the shape assumed by thestent in the strained state. The stent is positioned in the strainedstate through a perforation of the defect 6. Once installed the stentrestores its original shape, whereby its end portions open up to theirmaximum diameter and are fixed outside the defect 6.

[0053]FIG. 5 presents a stent embodiment applicable in the case of ananeurysmal dilatation of a blood vessel. The stent is provided withb theadditionally interwoven threads 1 on a section 8, which features ahigher interlacing density of the threads 1. This results in anaccelerated neointima formation and in exclusion of an aneurysmal cavity9 from the blood stream along a vessel 10.

[0054] The herein-proposed stent operates as follows. A preliminarycatheterization of the afferent passages is performed under asepticconditions. A guide wire is inserted into the catheter, and the guidewire working end is placed outside the zone of reconstruction.

[0055] Then the catheter is withdrawn, whereupon the stent and thedelivery system are fitted in succession onto the free guide wire end,said delivery system appearing as two coaxial catheters. Next the stentis deformed by applying slight longitudinal forces to the stent ends,after which the thus-strainde stent is placed into the free space of theoutside catheter of the delivery system. Further on the assembleddelivery system is brought to the place of endoreconstruction underfluoroscopy control and is released. The stent assumes its originalshape and is fixed reliably in position.

[0056] Thus, the stent construction provides for its quick andconvenient implantation in the preset zone of reconstruction.

Industrial Applicability

[0057] The proposed invention is instrumental in attaining high-qualityreliable endoprosthesizing of blood vessels, ducts, and perforatingdefects of the various organs, which is confirmed by good clinicaleffects attained in implantation of the stents in cases ofocclusion-stenotic pathology of the blood vessels, vascular aneurysms,obstructions of the billiary ducts, and in portal hypertension (TIPS).

[0058] The aforelisted surgeries were conducted in St.Petersburg in1992-1994 on the basis of the Central Roentgenology and RadiologyResearch Institute, the St.Petersburg State Medical Academy, as well onthe basis of the Central Regional Clinical Hospital.

1. A stent shaped as a three-dimensional body whose surface is formed byat least two groups of turns (2 and 3) made of interlaced elasticthreads and arranged along helical lines having opposite senses ofhelix, and the end faces of said three-dimensional body are formed bysections (5) where the turns of one helical line pass into the turns ofthe other helical line, CHARACTERIZED in that each of said sections ofpassing the turns of the helical lines is formed by a bend of a segmentof a single elastic thread (1) from which the turns of helical lines aremade.
 2. A stent as set forth in claim 1, CHARACTERIZED in that theturns of all helical lines are made of a single segment of the thread(1).
 3. A stent as set forth in claim 1 or 2, CHARACTERIZED in that theturns, (2 and 3) of helical lines are arranged with a variable pitch. 4.A stent as set forth in any one of claims 1-3, CHARACTERIZED in that thethree-dimensional body has a variable transverse diameter.
 5. A stent asset forth in any one of claims 1-4, CHARACTERIZED in that a presetsection (8) of the three-dimensional body is provided with theadditionally interwoven threads (1).
 6. A stent according to any one ofclaims 1-5, CHARACTERIZED in that free ends (4) of the threads (1) arejoined to the threads (1) that form the helical turns, and/or to oneanother.
 7. A stent according to any one of claims 1-6, CHARACTERIZED inthat on the sections (5) where the turns of one helical line pass intothose of the other helical line having the opposite sense of helix.
 8. Astent according to any one of claims 1-7, CHARACTERIZED in that thebending points on the sections (5) where the turns (2 and 3) merge, aresituated in different transverse planes relative to the longitudinalaxis of the three-dimensional body.
 9. A stent according to any one ofclaims 1-8, CHARACTERIZED in that the threads (1) are made of a materialfeaturing the shape memory effect.
 10. A stent according to any one ofclaims 1-8, CHARACTERIZED in that the threads (1) are made of asuperelastic material.
 11. A stent according to any one of claims 1-8,CHARACTERIZED in that the three-dimensional body has a coating of abiocompatible material.